The fundamental requirement of a shutter system is to provide a complete mechanical blockage of an energy source, such as light. What distinguishes shutter systems from other electromagnetic modulation devices is the use of a straight-through clearance aperture having no optical surfaces to modify the electromagnetic wave front. Typically, shutter systems are designed to function as either safety interlocks, as modulators, or in both capacities depending on the intended application.
When used as a safety interlock in an application such as a laser system, the shutter is used to block and absorb the laser beam whenever the laser's control system receives a request to establish a safe condition. A typical control system is comprised of a DC power supply, a relay or solid state device that switches the actuator which drives the shutter mechanism, and associated microprocessor based logic components. An example of such a control system is described in U.S. Pat. No. 4,513,345, incorporated herein by reference.
Generally, shutter systems are mounted directly to the output port of the laser head, or in some cases a separate housing is constructed to enclose the laser output and shutter mechanism, thereby serving to prevent access to the laser beam. The properties of a shutter system, particularly those used in conjunction with a laser system, require that they absorb all of the incident beam energy, with very little back scattering. Most prior art designs have sought to contain the resulting back scatter by utilizing a simple enclosure to allow absorption of the back scatter energy into the laser head and associated laser components contained in the enclosure. Two of the problems associated with this type of design are feedback of scattered energy into the optical system and the increased risk of leakage from the enclosure, thereby creating a safety hazard. As optical power levels escalate, these considerations become increasingly important from a design perspective.
An example of a well-known magnetic flexure type shutter is depicted in FIG. 1, which includes a very thin flexible foil 2 which is deflected into a beam path 4 by an electromagnet 6. The foil 2 is seen as being attached at one end to a collar 8 by a retaining screw 10, and lies parallel to and below the beam path 4 when the electromagnet is inactive. The electromagnet is of conventional design, having a ferrite core 12 surrounded by a magnetic winding 14 on a pancake bobbin. In operation, the winding 14 is energized, thereby activating the magnet 6 and causing the free end 2' of foil 2 to be attracted to magnet 6, moving across beam path 4. As foil 2 intercepts the beam path, the beam is reflected away at an increasing angle of reflection as foil end 2' moves into a biased position adjacent the magnet 6. In the full, closed position, as shown in FIG. 1, the foil conforms flat as it biases against the magnet, bending into an "S" shape as it approaches the retaining screw 10, providing an incident angle of about 50.degree. to 60.degree. for beam interception.
The foil 2 is extremely thin to allow for the required flexibility to enable the foil to contort into the "S" configuration. This required thinness, however, is inherently weak, particularly at stress points in the "S" shaped bends, and is also not thermally suitable for conducting away heat resulting from absorption of higher power lasers. Another aspect of the foil arrangement is that the foil reflects the light beam at an angle near that of the unaltered beam path, resulting in unwanted stray reflection lines appearing at the target plane as the foil end 2' begins to intercept the beam, continuing until the foil end is flat-biased against the magnet. Since the reflection is at a very narrow angle with respect to the unaltered beam path 4, the reflection cannot be eliminated in the device, and the fully closed "S" shape allows for a back scattering of laser light, whose effects as previously discussed are undesirable, from a safety standpoint and also from a component standpoint. This is due primarily as a result of the absorbed back scattered energy, and the contaminating of the exposed optics, including the shutter's own reflective mirror, as a result of this out gassing.